1. FIELD OF THE INVENTION
This invention relates to screen printing machines of the cylinder-type and particularly, to a screen printing machine that operates effectively with relatively stiff sheet material.
2. PRIOR ART
Screen printing machines of the cylinder-type have become increasingly popular for the reason that they are capable of high speed operation and precise registration for high quality color printing. In a typical prior art screen printing machine of the cylinder-type, a screen frame is horizontally mounted upon a reciprocating transport mechanism located above a cylinder. The cylinder functions as a printing platen.
The transport mechanism and the cylinder move in synchronism while a sheet of the stock material passes between the cylinder and that part of the screen engaged by a squeegee. In order to feed the sheet stock material to the print station, it is first advanced along an inclined bed until its leading edge contacts releasable stops. The cylinder then reverses and returns to its start position as grippers mounted on the cylinder close on the stock material. The transport mechanism and cylinder start movement in synchronism after the stops are operatively retracted. After an initial movement, the grippers release, allowing the sheet material to fall along a downwardly inclined receiving bed. The cylinder continues to move in synchronism with the transport mechanism. The remainder of the sheet material feed through. The cylinder reverses at the start of the next cycle to pick up the next sheet of material and the cycle of operation repeats.
If the stock material is relatively rigid, it resists the imposition of curvature. Thus the consequent stress due to bending reduces both the refinement and registry required for quality printing. Because of this resistance to curvature and the possible damage to rigid stock materials that may very well result, conventional cylinder-type screen printing machines are unsuitable. Consequently, rigid stock materials have had to be processed by hand one at a time in planar screen printing structures which are cumbersome and time-consuming to operate. The most relevant prior art known to the applicant includes the following:
U.S. Pat. No. 3,081,698: Childress et al.
U.S. Pat. No. 3,306,197: Jensen et al.
U.S. Pat. No. 3,318,236: Mueller
U.S. Pat. No. 3,538,846: Jaffa et al.
U.S. Pat. No. 3,675,571: Vertegaal
U.S. Pat. No. 3,774,537: Ichinose
U.S. Pat. No. 3,889,595: Jaffa
U.S. Pat. No. 3,921,519: Zimmer
U.S. Pat. No. 3,998,156: Zimmer
U.S. Pat. No. 4,176,601: Szarka
U.S. Pat. No. 4,448,124: Nagatani
U.S. Pat. No. 4,509,422: Nagatani
U.S. Pat. No. 3,538,846 to Jaffa et al is particularly directed to a sheet ejector system for printing machines, and provides a conveyor mounted to a table base in adjacently extending relation to a table. There are a multiplicity of parallel spaced apart endless belts which pass over an idler roller positioned remote from the table. Switching and sequencing logic circuitry is provided and a carriage is raised with suction grippers positioned toward the table to grip a sheet mounted thereon. When the carriage is in the raised position, suction grippers are moved between the belts and away from the table in order to drag or pull the sheet onto the belts.
U.S. Pat. No. 3,318,236 to Mueller is directed to an electrostatic drum printer, relating to a limited flexibility stock for printing. In this reference, sheets are formed of plywood and a shaft is spaced above a horizontally extending row of rollers of a roller conveyor. The rollers are generally parallel with the shaft and are rotatively supported at their ends by the bearings on frame members.
U.S. Pat. No. 3,921,519 to Zimmer is directed to a rotary printing machine which includes a plurality of rotating printing cylinders. A web of material is supported on a printer's blanket which is moved and guided over guide rollers.
U.S. Pat. No. 3,889,595 to Jaffa is directed to a continuous rotary screen printing system and provides for a frame assembly which has a pair of end rollers journalled adjacent the end portions of a frame assembly. An endless belt/printing blanket passes over the end rollers. An upper flight of the endless belt provides for a movable printing bed for supporting the material to be printed.
U.S. Pat. No. 4,176,601 to Szarka is directed to what is termed an automated towel transfer printing/feeding/drying/folding apparatus. They provide a conveyor system having an endless printing belt for supporting and indexing a workpiece during the screen printing operation. They include a transfer apparatus which is located adjacent the discharge end of the indexing printing belt and such includes a removing system in the form of belt strips having gripping pins to peel and remove the workpiece from the printing belt.